In voice communications, in order to ensure call quality and equipment safety, echo cancellation is usually carried out. In the currently used echo cancellation methods, when the transmitting terminal signal and the receiving terminal signal are known, an echo path filter and an echo signal are calculated by these two signals and then the echo signal is cancelled from the transmitting terminal signal to prevent the communication from being interfered with echoes.
However, since most of today's communications have been digitalized, the transmitting and receiving terminal signals are both digitally transmitted. Transmitting and receiving terminal signals may have a sampling rate mismatch due to different sampling clocks, which will decrease the estimation accuracy of the echo path filter and the echo signal, resulting in degradation in the performance of echo cancellation.
In order to reduce or eliminate the impact of the sampling rate mismatch on the echo cancellation performance, it is required to calculate the sampling rate mismatch between the transmitting and receiving terminal signals and correct it before the echo is cancelled. For the calculation of the sampling rate mismatch, the existing practice is to calculate the sampling rate mismatch between the two terminals by the statistics of sampling clock cycles of the transmitting and receiving terminal signals in a period of time, or to calculate the sampling rate mismatch using a pure algorithm approach within a pre-set variation range of sampling rate mismatch, the sampling rate mismatch being within 20 Hz by default. After the sampling rate mismatch is calculated, the existing practice is usually to send the calculated sampling rate mismatch to an echo cancellation filter, and an echo cancellation system adjusts it accordingly such that the sampling rate mismatch is corrected, thereby ensuring the echo cancellation effect.
The existing practice for sampling rate mismatch correction at least has the following drawbacks:
When calculating the sampling rate mismatch, the existing practice requires monitoring the sampling clocks of the transmitting and receiving terminals, and in some cases, special hardware is also needed, such as a CPU with high-qualified performance. Thus, it has a higher requirement of hardware. Besides, the calculation is more complicated, and more storage resources are occupied. In addition, the existing practice is not immediately directed to the signals for sampling rate mismatch correction. Instead, it merely transmits the sampling rate mismatch to an echo cancellation system to adjust and process the deviation by the echo cancellation system. The manner of adjusting mismatch by an echo cancellation system increases the burden of the system and affects the echo cancellation effect.